Nonvolatile semiconductor storage device and manufacturing method thereof

ABSTRACT

An object of the present invention is to provide a nonvolatile semiconductor storage device with a superior charge holding characteristic in which highly-efficient writing is possible at low voltage, and to provide a manufacturing method thereof. 
     The nonvolatile semiconductor storage device includes a semiconductor film having a pair of impurity regions formed apart from each other and a channel formation region provided between the impurity regions; and a first insulating film, a charge accumulating layer, a second insulating film, and a conductive film functioning as a gate electrode layer which are provided over the channel formation region. In the nonvolatile semiconductor storage device, a second barrier formed by the first insulating film against a charge of the charge accumulating layer is higher in energy than a first barrier formed by the first insulating film against a charge of the semiconductor film.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a nonvolatile semiconductor storagedevice that is electrically writable, readable, and erasable, and itsmanufacturing method. In particular, the present invention relates to astructure of a charge accumulating layer in the nonvolatilesemiconductor storage device.

2. Description of the Related Art

The market is expanding for nonvolatile memories as one kind ofsemiconductor memories, in which data can be electrically rewritten anddata can be stored even after the power is turned off. Features of anonvolatile memory lie in that its structure is similar to that of a MOStransistor and a region capable of accumulating charges for a longperiod of time is provided over a channel formation region. A floatinggate type nonvolatile memory holds charges by injecting the charges in afloating gate through a tunnel insulating film over a channel formationregion. In a MONOS (Metal-Oxide-Nitride-Oxide Semiconductor) typenonvolatile memory, a trap or a silicon cluster of a silicon nitridefilm is used as a charge holdback carrier.

FIG. 16 shows a typical structure of a nonvolatile memory. Over asemiconductor film 800 forming a channel formation region, a nonvolatilememory has a first insulating film 801 which is also called a tunnelinsulating film, a charge accumulating layer 802 which is also called afloating gate, a second insulating film 803, a control gate electrode804, a source 805, and a drain 806.

Such a nonvolatile memory can store one-bit data by one transistor. In acase of writing data, voltage is applied between the source 805 and thedrain 806 and between the semiconductor film 800 and the control gateelectrode 804 to inject charges from the semiconductor film 800 to thecharge accumulating layer 802 through the first insulating film 801;then, the charges are accumulated in the charge accumulating layer 802that is electrically insulated from its periphery. In a case of readingdata, information can be read out by utilizing a characteristic thatthreshold voltage of a MOS transistor changes depending on whether thereare charges in the charge accumulating layer 802. That is to say, theinformation of “0” and “1” can be stored and read. In a case of erasingdata, on the contrary, high voltage is applied to the semiconductor film800 or the source 805 so as to extract the charges from the chargeaccumulating layer 802 through the first insulating film 801.

The charges are injected in the charge accumulating layer 802 byincreasing voltage applied between the semiconductor film 800 and thecontrol gate electrode 804 and using hot electrons (NOR type) orFowler-Nordheim type (F-N type) tunnel current (NAND type) flowingthrough the first insulating film 801 by an intense electric field. Inthe both types, a high electric field is applied between thesemiconductor film 800 and the control gate electrode 804; therefore,the charges are injected in the insulating film that is formed to bethin.

The nonvolatile memory having the charge accumulating layer 802 isrequired to have a characteristic that can hold charges accumulated inthe charge accumulating layer 802 for ten years or more in order toassure the reliability. Therefore, the first insulating film 801 and thesecond insulating film 803 are required to have a high insulatingproperty so that the charges do not leak from the charge accumulatinglayer 802. A floating gate type nonvolatile memory has difficulty inthinning the first insulating film 801 so that F-N type tunnel currentflows therethrough (7 to 8 nm thick in a case of a SiO₂ film) and it isdifficult to reduce writing voltage and erasing voltage (10 to 20 V). Inaddition, a MONOS type nonvolatile memory is required to have a siliconnitride film with a comparatively large volume so that a trap or asilicon cluster in the silicon nitride film holds the charge andthreshold voltage of a MOS transistor is changed. Thus, it is consideredthat element miniaturization and voltage reduction have limitation.

A nonvolatile memory in which the second insulating film 803 in FIG. 16is formed by a plurality of insulating films and a deep trap level isprovided at high concentration in order to reduce writing voltage andimprove a charge holding characteristic is known (for example, Reference1: Japanese Published Patent Application No. H11-40682). Moreover, aMONOS type nonvolatile memory in which a charge holding characteristicis improved by controlling hydrogen concentration of silicon nitrideused for the charge accumulating layer 802 is known (for example,Reference 2: Japanese Published Patent Application No. 2004-221448).

SUMMARY OF THE INVENTION

Even though the second insulating film 803 and the charge accumulatinglayer 802 in FIG. 16 are improved, thinning the first insulating film801 is necessary in order to maintain the charge holding characteristic.However, thinning the first insulating film 801 has limitation, causinga problem in that writing voltage cannot be reduced if the thickness ofthe insulating film 801 cannot be thinned. Moreover, improvement of onlythe charge holding characteristic of the charge accumulating layer 802could not allow the reduction of writing voltage.

Further, it is difficult to use a thermal oxidation method in theformation of the insulating films when the nonvolatile semiconductorstorage device is formed over a substrate having low heat resistancesuch as a glass substrate by using an element such as a thin filmtransistor. Therefore, in a case of forming the first insulating film801 to be thin, it was necessary to form the insulating film with athickness of several nanometers by a CVD method or a sputtering method.However, since the first insulating film 801 formed with a thickness ofseveral nanometers by a CVD method or a sputtering method does not haveenough film quality because of a defect inside the film, there areproblems in that leak current is generated and the semiconductor film800 and the charge accumulating layer 802 are short-circuited, or thelike, resulting in that the reliability of the nonvolatile semiconductorstorage device is lowered (a writing or reading defect).

In view of the aforementioned problems, it is an object of the presentinvention to provide a nonvolatile semiconductor storage device which issuperior in a charge holding characteristic and in whichhighly-efficient writing is possible at low voltage, and itsmanufacturing method.

A nonvolatile semiconductor storage device of the present inventionincludes a semiconductor film having a pair of impurity regions formedapart from each other and a channel formation region provided betweenthe pair of impurity regions; and a first insulating film, a chargeaccumulating layer, a second insulating film, and a conductive filmfunctioning as a gate electrode layer which are provided over thechannel formation region. In this nonvolatile semiconductor storagedevice, a second barrier formed by the first insulating film against acharge of the charge accumulating layer is higher in energy than a firstbarrier formed by the first insulating film against a charge of thesemiconductor film.

A nonvolatile semiconductor storage device of the present inventionincludes a semiconductor film having a pair of impurity regions formedapart from each other and a channel formation region provided betweenthe pair of impurity regions; and a first insulating film, a chargeaccumulating layer, a second insulating film, and a conductive filmfunctioning as a gate electrode layer which are provided over thechannel formation region. In this nonvolatile semiconductor storagedevice, the charge accumulating layer is formed of a material with asmaller energy gap (band gap) or higher electron affinity than thesemiconductor film.

A method for manufacturing a nonvolatile semiconductor storage device ofthe present invention includes: forming a semiconductor film over asubstrate; forming a first insulating film including one or both ofoxygen and nitrogen on a surface of the semiconductor film by performinghigh-density plasma treatment; forming a charge accumulating layerincluding a material with a smaller energy gap or higher electronaffinity than the semiconductor film, over the first insulating film;forming a second insulating film including nitrogen over the chargeaccumulating layer; forming a conductive film over the second insulatingfilm; forming selectively a resist over the semiconductor film; removingselectively the first insulating film, the charge accumulating layer,the second insulating film, and the conductive film, thereby leaving thefirst insulating film, the charge accumulating layer, the secondinsulating film, and the conductive film so as to overlap with at leasta part of the semiconductor film; and forming an impurity region in thesemiconductor film by introducing an impurity element with a left partof the conductive film used as a mask.

A method for manufacturing a nonvolatile semiconductor storage device ofthe present invention includes: forming a semiconductor film over asubstrate; forming a first insulating film including a stacked-layerfilm of an oxide film and a film including oxygen and nitrogen on asurface of the semiconductor film by performing first high-densityplasma treatment under an oxygen atmosphere and then performing secondhigh-density plasma treatment under a nitrogen atmosphere; forming acharge accumulating layer including a material with a smaller energy gapor higher electron affinity than the semiconductor film, over the firstinsulating film; forming a second insulating film including nitrogenover the charge accumulating layer; oxidizing a surface of the secondinsulating film including nitrogen by performing third high-densityplasma treatment under an oxygen atmosphere; forming a conductive filmover the second insulating film of which surface has been oxidized;removing selectively the first insulating film, the charge accumulatinglayer, the second insulating film, and the conductive film, therebyleaving the first insulating film, the charge accumulating layer, thesecond insulating film, and the conductive film so as to overlap with atleast a part of the semiconductor film; and forming an impurity regionin the semiconductor film by introducing an impurity element with a leftpart of the conductive film used as a mask.

A method for manufacturing a nonvolatile semiconductor storage device ofthe present invention includes: forming a first semiconductor film and asecond semiconductor film over a substrate; forming a first insulatingfilm on a surface of the first semiconductor film and a surface of thesecond semiconductor film by performing first high-density plasmatreatment under an oxygen atmosphere and then performing secondhigh-density plasma treatment under a nitrogen atmosphere; forming acharge accumulating layer including a material with a smaller energy gapor higher electron affinity than the first semiconductor film and thesecond semiconductor film, over the first insulating film; forming asecond insulating film including nitrogen over the charge accumulatinglayer; removing selectively the first insulating film, the chargeaccumulating layer, and the second insulating film which are formed overthe second semiconductor film so as to expose a surface of the secondsemiconductor film; oxidizing a surface of the second insulating filmincluding nitrogen formed over the first semiconductor film andsimultaneously forming a gate insulating film on the surface of thesecond semiconductor film, by performing third high-density plasmatreatment under an oxygen atmosphere; forming a conductive film over thesecond insulating film of which surface has been oxidized and over thegate insulating film; removing selectively the first insulating film,the charge accumulating layer, the second insulating film, the gateinsulating film, and the conductive film, thereby leaving the firstinsulating film, the charge accumulating layer, the second insulatingfilm, and the conductive film so as to overlap with at least a part ofthe first semiconductor film and leaving the gate insulating film andthe conductive film so as to overlap with at least a part of the secondsemiconductor film; and forming an impurity region in the firstsemiconductor film and the second semiconductor film by introducing animpurity element with a left part of the conductive film used as a mask.

In the nonvolatile semiconductor storage device of the presentinvention, the semiconductor film may be formed over a substrate havingan insulating surface. Also, in the nonvolatile semiconductor storagedevice of the present invention, the pair of the impurity regions andthe channel formation region may be formed in a single crystal siliconsubstrate.

It is to be noted that the high-density plasma treatment means plasmatreatment performed under conditions where high frequency is used,electron density ranges from 1×10¹¹ cm⁻³ to 1×10¹³ cm⁻³, and electrontemperature ranges from 0.5 eV to 1.5 eV.

In a case of forming the charge accumulating layer over thesemiconductor film with an insulating film functioning as a tunnel oxidefilm interposed therebetween, charge injection from the semiconductorfilm to the charge accumulating layer can be made easier and chargedisappearance from the charge accumulating layer can be prevented byhaving a structure in which a second barrier formed by the insulatingfilm against a charge of the charge accumulating layer is higher inenergy than a first barrier formed by the insulating film against acharge of the semiconductor film.

In the case of forming the charge accumulating layer over thesemiconductor film with the insulating film functioning as a tunneloxide film interposed therebetween, charge injection from thesemiconductor film to the charge accumulating layer can be made easierand charge disappearance from the charge accumulating layer can beprevented by forming the charge accumulating layer using a material witha smaller energy gap or higher electron affinity than a material usedfor the semiconductor film. Accordingly, it becomes possible tomanufacture a nonvolatile semiconductor storage device which enableshighly-efficient writing at low voltage and which is superior in acharge holding characteristic and has high reliability.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1E show an example of a manufacturing method of anonvolatile semiconductor storage device of the present invention;

FIGS. 2A to 2E show an example of a manufacturing method of anonvolatile semiconductor storage device of the present invention;

FIGS. 3A to 3C show an example of a manufacturing method of anonvolatile semiconductor storage device of the present invention;

FIGS. 4A to 4D show an example of a manufacturing method of anonvolatile semiconductor storage device of the present invention;

FIGS. 5A to 5C show an example of a manufacturing method of anonvolatile semiconductor storage device of the present invention;

FIGS. 6A and 6B show an example of a manufacturing method of anonvolatile semiconductor storage device of the present invention;

FIGS. 7A and 7B show examples of an apparatus for manufacturing anonvolatile semiconductor storage device of the present invention;

FIG. 8 shows an example of a nonvolatile semiconductor storage device ofthe present invention;

FIGS. 9A to 9C show an example of a manufacturing method of anonvolatile semiconductor storage device of the present invention;

FIGS. 10A to 10C show an example of a manufacturing method of anonvolatile semiconductor storage device of the present invention;

FIGS. 11A to 11C show an example of a manufacturing method of anonvolatile semiconductor storage device of the present invention;

FIGS. 12A and 12B show an example of a nonvolatile semiconductor storagedevice of the present invention;

FIGS. 13A to 13C show examples of usage of a nonvolatile semiconductorstorage device of the present invention;

FIGS. 14A to 14H show examples of usage of a nonvolatile semiconductorstorage device of the present invention;

FIGS. 15A and 15B explain movement of charges in a nonvolatilesemiconductor storage device of the present invention; and

FIG. 16 shows an example of a conventional nonvolatile semiconductorstorage device.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment modes of the present invention are hereinafter described withreference to drawings. However, it is easily understood by those skilledin the art that the present invention is not limited by the followingdescription and that the mode and detail can be variously changedwithout departing from the scope and spirit of the present invention.Therefore, the present invention is not construed as being limited tothe description of the embodiment modes hereinafter shown. In thestructure of the present invention described below, a reference numeraldenoting the same part may be used in common throughout the drawings.

Embodiment Mode 1

Embodiment Mode 1 will explain an example of a nonvolatile semiconductorstorage device with reference to drawings. It is to be noted that a caseis shown here in which a storage element included in a memory portion ofa nonvolatile semiconductor storage device is formed at the same time asan element such as a transistor included in a logic portion that isformed over the same substrate as the memory portion and that carriesout control and the like of writing and reading of the storage element.

First, island-shaped semiconductor films 103 a and 103 b are formed overa substrate 101 with an insulating film 102 interposed therebetween(FIG. 1A). The island-shaped semiconductor films 103 a and 103 b can beprovided in such a way that (1) an amorphous semiconductor film isformed of a material containing silicon (Si) as its main component (forexample, Si_(x)Ge_(1-x) or the like) by a sputtering method, an LPCVDmethod, a plasma CVD method, or the like over the insulating film 102formed in advance over the substrate 101; (2) the amorphoussemiconductor film is crystallized; and then (3) the crystallizedsemiconductor film is selectively etched. It is to be noted that theamorphous semiconductor film can be crystallized by a lasercrystallization method, a thermal crystallization method using RTA or anannealing furnace, a thermal crystallization method using a metalelement promoting crystallization, a method in which these are combined,or the like.

As the substrate 101, a glass substrate, a quartz substrate, a metalsubstrate (such as a stainless steel substrate), a ceramic substrate, ora semiconductor substrate such as a Si substrate can be used. Inaddition, as a plastic substrate, a substrate formed of polyethyleneterephthalate (PET), polyethylene naphthalate (PEN), polyether sulfone(PES), acrylic, or the like can be used.

The insulating film 102 is formed of an insulating material such assilicon oxide (SiO_(x)), silicon nitride (SiN_(x)), silicon oxynitride(SiO_(x)N_(y), x>y>0), or silicon nitride oxide (SiN_(x)O_(y), x>y>0),by CVD method, spattering method or the like. For example, in a casewhere the insulating film 102 has a two-layer structure, a siliconnitride oxide film may be formed as a first insulating film and asilicon oxynitride film may be formed as a second insulating film.Alternatively, a silicon nitride film may be formed as the firstinsulating film and a silicon oxide film may be formed as the secondinsulating film. By forming the insulating film 102 functioning as ablocking layer in this manner, it is possible to prevent alkaline earthmetal or alkali metal such as Na in the substrate 101 from adverselyaffecting an element to be formed over the insulating film 102. In acase of using quartz for the substrate 101, the insulating film 102 maybe omitted.

Next, oxidation treatment, nitridation treatment, or oxynitridationtreatment is performed on the semiconductor films 103 a and 103 b byhigh-density plasma treatment, thereby forming a first insulating film104 which becomes an oxide film, a nitride film, or a film includingoxygen and nitrogen on surfaces of the semiconductor films 103 a and 103b (the first insulating film 104 is hereinafter referred to as theinsulating film 104) (FIG. 1B).

For example, in a case of performing oxidation treatment or nitridationtreatment when the semiconductor films 103 a and 103 b each containsilicon as its main component, a silicon oxide film or a silicon nitridefilm is formed as the insulating film 104. Moreover, after performingoxidation treatment on the semiconductor films 103 a and 103 b byhigh-density plasma treatment, nitridation treatment may be performed byconducting high-density plasma treatment again. In the latter case, asilicon oxide film is formed in contact with the semiconductor films 103a and 103 b and a film including oxygen and nitrogen is formed over thesilicon oxide film, thereby forming a stack of the silicon oxide filmand the film including oxygen and nitrogen as the insulating film 104.

Here, the insulating film 104 is formed with a thickness of 1 to 10 nm,preferably 1 to 5 nm. For example, after forming a silicon oxide filmwith a thickness of about 5 nm on surfaces of the semiconductor films103 a and 103 b by performing oxidation treatment on the semiconductorfilms 103 a and 103 b by high-density plasma treatment, a film includingoxygen and nitrogen with a thickness of about 2 nm is formed on asurface of the silicon oxide film by high-density plasma treatment. Inthis case, the silicon oxide film formed on the surfaces of thesemiconductor films 103 a and 103 b has a thickness of about 3 nm. Thisis because the thickness of the silicon oxide film is reduced from thethickness of the formed film including oxygen and nitrogen. Moreover, atthis time, the oxidation treatment and the nitridation treatment byhigh-density plasma treatment are preferably performed continuouslywithout exposure to the air. By continuously performing the high-densityplasma treatment, prevention of impurity mixture and improvement ofproduction efficiency can be achieved.

In a case of oxidizing the semiconductor films by high-density plasmatreatment, the treatment is performed under an oxygen atmosphere. As theoxygen atmosphere, for example, an atmosphere including oxygen (O₂) anda noble gas; an atmosphere including dinitrogen monoxide (N₂O) and anoble gas; an atmosphere including oxygen, hydrogen (H₂), and a noblegas; or an atmosphere including dinitrogen monoxide, hydrogen (H₂), anda noble gas is given. As the noble gas, at least one of He, Ne, Ar, Kr,and Xe is included. On the other hand, in a case of nitriding thesemiconductor films by high-density plasma treatment, the treatment isperformed under a nitrogen atmosphere. As the nitrogen atmosphere, forexample, an atmosphere including nitrogen (N₂) and a noble gas; anatmosphere including nitrogen, hydrogen, and a noble gas; or anatmosphere including NH₃ and a noble gas is given. As the noble gas, atleast one of He, Ne, Ar, Kr, and Xe is included.

As the noble gas, for example, Ar can be used. Alternatively, a gas inwhich Ar and Kr are mixed may be used. In a case of performinghigh-density plasma treatment in a noble gas atmosphere, the insulatingfilm 104 may include the noble gas (at least one of He, Ne, Ar, Kr, andXe) used for the plasma treatment. When Ar is used, the insulating film104 may include Ar.

Moreover, the high-density plasma treatment is performed in anatmosphere including the aforementioned gas with an electron density of1×10¹¹ cm⁻³ or more and plasma electron temperature of 1.5 eV or less.More specifically, the electron density ranges from 1×10¹¹ cm⁻³ to1×10¹³ cm⁻³ and the plasma electron temperature ranges from 0.5 eV to1.5 eV. Since the plasma electron density is high and the electrontemperature in the vicinity of an object to be processed that is formedover the substrate 101 (here, the semiconductor films 103 a and 103 b)is low, plasma damage on the object to be processed can be prevented.Moreover, since the plasma electron density is as high as 1×10¹¹ cm⁻³ ormore, an oxide film or a nitride film formed by oxidizing or nitridingthe object to be processed by using the plasma treatment can be denseand superior in uniformity of its film thickness and the like ascompared with a film formed by a CVD method, a sputtering method, or thelike. Furthermore, since the plasma electron temperature is as low as1.5 eV or less, oxidation treatment or nitridation treatment can beperformed at lower temperature than in conventional plasma treatment orthermal oxidation method. For example, even plasma treatment attemperatures lower than the distortion point of a glass substrate by100° C. or more can sufficiently perform oxidation treatment ornitridation treatment. As the frequency for forming plasma, highfrequency such as a microwave (for example, 2.45 GHz) can be used.

In this embodiment mode, the insulating film 104 formed over thesemiconductor film 103 a in the memory portion will function as a tunneloxide film in a storage element to be completed later. Therefore, thethinner the insulating film 104 is, the more easily the tunnel currentflows, which allows a higher-speed operation as a memory. Further, whenthe insulating film 104 is thinner, charges can be accumulated at lowervoltage in a charge accumulating layer to be formed later; therefore,the power consumption of the semiconductor device can be reduced.Accordingly, the insulating film 104 is preferably formed to be thin.

In general, a thermal oxidation method is given as a method for forminga thin insulating film over a semiconductor film. However, when astorage element is provided over a substrate of which melting point isnot sufficiently high, such as a glass substrate, it is very difficultto form the insulating film 104 by a thermal oxidation method. Moreover,an insulating film formed by a CVD method or a sputtering method doesnot have enough film quality because of a defect inside the film,causing a problem in that a defect such as a pinhole is produced whenthe film is formed to be thin. In addition, an insulating film formed bya CVD method or a sputtering method does not cover an end portion of thesemiconductor film sufficiently, resulting in that a conductive film andthe like to be later formed over the insulating film 104 and thesemiconductor film may be in contact with each other to cause leakage.Thus, when the insulating film 104 is formed by the high-density plasmatreatment as shown in this embodiment mode, the insulating film 104 canbe denser than an insulating film formed by a CVD method, a sputteringmethod, or the like, and moreover the insulating film 104 can cover anend portion of the semiconductor film sufficiently. As a result, theoperation speed as a memory can be increased and the power consumptionof the semiconductor device can be reduced.

Next, a charge accumulating layer 105 is formed over the insulating film104 (FIG. 1C). The charge accumulating layer 105 functions as a layeraccumulating charges in a storage element to be completed later and mayalso be referred to as a floating gate in general. The chargeaccumulating layer 105 is preferably formed of a material with a smallerenergy gap (band gap) than the material used for the semiconductor films103 a and 103 b. For example, the charge accumulating layer 105 can beformed of germanium (Ge), a silicon-germanium alloy, or the like. Inaddition, the charge accumulating layer 105 can be formed by usinganother conductive film or semiconductor film as long as a material hasa smaller energy gap (band gap) than the material used for thesemiconductor films 103 a and 103 b. Furthermore, the chargeaccumulating layer 105 may be formed of a material with higher electronaffinity than the material used for the semiconductor films 103 a and103 b.

Here, the charge accumulating layer 105 is formed using a filmcontaining germanium as its main component with a thickness of 1 to 20nm, preferably 5 to 10 nm, in an atmosphere including a germaniumelement (for example, GeH₄) by a plasma CVD method. When thesemiconductor film is formed of a material containing Si as its maincomponent and the film including germanium with a smaller energy gapthan Si is provided as the charge accumulating layer over thesemiconductor film with the insulating film functioning as a tunneloxide film interposed therebetween in this manner, a second barrierformed by the insulating film against a charge of the chargeaccumulating layer gets higher in energy than a first barrier formed bythe insulating film against a charge of the semiconductor film. As aresult, the charge can be easily injected from the semiconductor film tothe charge accumulating layer, thereby preventing charge disappearancefrom the charge accumulating layer. That is to say, in a case ofoperating as a memory, highly-efficient writing is possible at lowvoltage and moreover, the charge holding characteristic can be improved.

Next, a second insulating film 107 including a silicon oxynitride film,a silicon nitride film, a silicon nitride oxide film, or the like isformed over the charge accumulating layer 105 (FIG. 1D). The insulatingfilm 107 can be formed by an LPCVD method, a plasma CVD method, or thelike, and here the insulating film 107 is formed by a silicon nitridefilm or a silicon nitride oxide film with a thickness of 1 to 20 nm,preferably 5 to 10 nm, by a plasma CVD method. Alternatively, the chargeaccumulating layer 105 may be subjected to high-density plasma treatmentto perform nitridation treatment so that a nitride film (for example,GeN_(x) in a case of using a film containing germanium as its maincomponent as the charge accumulating layer 105) is formed on a surfaceof the charge accumulating layer 105. In the latter case, the nitridefilm obtained by the nitridation treatment may be used as the insulatingfilm 107 or the aforementioned insulating film may be separately formedas the insulating film 107 over the nitride film obtained by thenitridation treatment. In addition, the second insulating film 107 maybe formed of aluminum oxide (AlO_(x)), hafnium oxide (HfO_(x)), ortantalum oxide (TaO_(x)).

In the aforementioned step, the charge accumulating layer 105 and theinsulating film 107 are preferably formed continuously without exposureto the air. By continuously forming the charge accumulating layer 105and the insulating film 107, prevention of impurity mixture andimprovement of production efficiency can be achieved. For example, thecharge accumulating layer 105 and the insulating film 107 are formedcontinuously without exposure to the air by using a plasma CVD method.

Next, after selectively forming a resist 108 so as to cover the elementincluded in the memory portion, the insulating film 104, the chargeaccumulating layer 105, and the insulating film 107 which are formedover the element included in the logic portion are selectively removed(FIG. 1E). Here, after selectively forming the resist 108 so as to coverthe insulating film 107 formed over the semiconductor film 103 a, theinsulating film 104, the charge accumulating layer 105, and theinsulating film 107 which are formed over the semiconductor film 103 bare selectively removed, thereby exposing the semiconductor film 103 b.

Next, oxidation treatment, nitridation treatment, or oxynitridationtreatment is performed by high-density plasma treatment (FIG. 2A). As aresult, an insulating film 110 is formed on a surface of the secondinsulating film 107 and an insulating film 109 is formed on a surface ofthe semiconductor film 103 b. Here, the insulating film 110 having afilm including oxygen and nitrogen (here, a silicon nitride oxide filmor a silicon oxynitride film) is formed on the surface of the insulatingfilm 107 by performing high-density plasma treatment under an oxygenatmosphere on the insulating film 107 formed by a silicon nitride filmor a silicon nitride oxide film. At the same time, the insulating film109 having a silicon oxide film is formed on the surface of thesemiconductor film 103 b. The insulating film 109 functions as a gateinsulating film. The second insulating film 107 may be covered with amask or the like so that the insulating film 110 is not formed. It is tobe noted that the high-density plasma treatment may be performed by acondition and a method similar to those for the high-density plasmatreatment performed on the semiconductor films 103 a and 103 b shown inFIG. 1B.

Moreover, in FIG. 2A, the insulating film 109 may be formed by a plasmaCVD method or the like instead of the high-density plasma treatment. Inthis case, the insulating film may or may not be formed over the secondinsulating film 107.

Subsequently, a conductive film is formed over the semiconductor films103 a and 103 b (FIG. 2B). Here, an example is shown in which a stack ofa conductive film 111 a and a conductive film 111 b is formed as theconductive film. Needless to say, the conductive film may have asingle-layer structure or a stacked-layer structure including three ormore layers.

The conductive films 111 a and 111 b can be formed of an elementselected from tantalum (Ta), tungsten (W), titanium (Ti), molybdenum(Mo), aluminum (Al), copper (Cu), chromium (Cr), niobium (Nb), and thelike or an alloy or compound material including any of these elements asits main component. Moreover, a semiconductor material typified bypolycrystalline silicon doped with an impurity element such asphosphorus can be used. Here, the conductive film 111 a is formed oftantalum nitride and the conductive film 111 b is formed of tungstenover the conductive film 111 a. In addition, the conductive film 111 acan be formed of tungsten nitride, molybdenum nitride, or titaniumnitride, and the conductive film 111 b can be formed of tantalum,molybdenum, titanium, or the like. The conductive films 111 a and 111 bcan be formed by combining these materials freely.

Next, a resist 112 is selectively formed over the conductive film 111 bformed over the semiconductor films 103 a and 103 b. Then, theinsulating film 104, the charge accumulating layer 105, the insulatingfilm 107, the insulating film 110, and the conductive films 111 a and111 b which are provided over the semiconductor film 103 a, and theinsulating film 109 and the conductive films 111 a and 111 b which areprovided over the semiconductor film 103 b are selectively removed byusing the resist 112 as a mask (FIG. 2C).

Next, an impurity element is introduced in the semiconductor film 103 aand the semiconductor film 103 b; thus, impurity regions 114 a which canfunction as source or drain regions are formed in the semiconductor film103 a and the semiconductor film 103 b and channel formation regions 114b are each formed between the impurity regions 114 a that are providedapart from each other (FIG. 2D). The impurity regions 114 a and thechannel formation regions 114 b can be formed in a self-aligning mannerby using conductive films 113 a and 113 b functioning as gate electrodesas a mask when the impurity element is introduced in the semiconductorfilms 103 a and 103 b.

Next, an insulating film is formed over the semiconductor films 103 aand 103 b and the conductive films 113 a and 113 b (FIG. 2E). Here, theinsulating film is formed by stacking an insulating film 115 a and aninsulating film 115 b. Alternatively, the insulating film may have asingle-layer structure or a stacked-layer structure including three ormore layers. After that, contact holes are selectively formed in theinsulating films 115 a and 115 b to expose the semiconductor films 103 aand 103 b, and then a conductive film 116 is selectively formed so as tofill the contact holes. The conductive film 116 is electricallyconnected to the impurity regions 114 a of the semiconductor films 103 aand 103 b.

By these steps, a nonvolatile semiconductor storage device having alogic portion and a storage element portion having a storage element canbe manufactured. In the manufacturing method shown in FIGS. 1A to 2E,the insulating film 104 and the insulating film 109 can be provided withdifferent thickness or formed of different materials.

Although this embodiment mode shows an example of forming a thin filmtransistor (TFT) by using the semiconductor film formed over thesubstrate, the nonvolatile semiconductor storage device of the presentinvention is not limited to this. For example, as shown in FIG. 8, afield effect transistor (FET) of which channel formation region isformed directly in a semiconductor substrate made of Si or the like maybe used.

A field effect transistor is formed on a single-crystal semiconductorsubstrate 301. In the single-crystal semiconductor substrate 301, nwells or p wells 302 which are separated by a field oxide film 303 areformed. When an n-type single-crystal semiconductor substrate is used,only p wells are preferably provided. Meanwhile, when a p-typesingle-crystal semiconductor substrate is used, only n wells arepreferably provided. Gate insulating films 304 and 305 are thin filmsformed by high-density plasma treatment or a thermal oxidation method.The charge accumulating layer 105, the insulating film 107, theinsulating film 110, the conductive films 113 a, 113 b, and 116, and thelike can be formed by the material and the method shown in thisembodiment mode.

As thus described, in the case of forming the charge accumulating layerover the semiconductor film with the insulating film functioning as atunnel oxide film interposed therebetween, the second barrier formed bythe insulating film against a charge of the charge accumulating layer ishigher in energy than the first barrier formed by the insulating filmagainst a charge of the semiconductor film. Thus, the charges can beeasily injected from the semiconductor film to the charge accumulatinglayer and charge disappearance from the charge accumulating layer can beprevented. Moreover, in the case of forming the charge accumulatinglayer over the semiconductor film with the insulating film functioningas a tunnel oxide film interposed therebetween, the provision of thecharge accumulating layer by using a material with a smaller energy gap(band gap) than the material used for the semiconductor film can make iteasier to inject the charges from the semiconductor film to the chargeaccumulating layer and can prevent charge disappearance from the chargeaccumulating layer. Accordingly, it becomes possible to manufacture anonvolatile semiconductor storage device which enables highly-efficientwriting at low voltage and which superior to charge holdingcharacteristic.

Embodiment Mode 2

Embodiment Mode 2 will explain charge injection and holding in thecharge accumulating layer in the memory portion of the nonvolatilesemiconductor storage device shown in the above embodiment mode, withreference to FIGS. 15A and 15B.

FIGS. 15A and 15B are band diagrams of the storage element of EmbodimentMode 1, showing a state in which the semiconductor film 103 a, the firstinsulating film 104, the charge accumulating layer 105, the secondinsulating film 107 (or a stacked film of the second insulating film 107and the insulating film 110), and the conductive film 113 a functioningas a gate electrode are stacked. FIGS. 15A and 15B show a case of usinga p-type semiconductor film as the semiconductor film 103 a.

FIG. 15A shows a case in which voltage is not applied to the conductivefilm 113 a and in which the Fermi level Ef of the semiconductor film 103a is equal to the Fermi level Efm of the conductive film 113 a. FIG. 15Bshows a case in which electrons are held in the charge accumulatinglayer 105 by applying voltage to the conductive film 113 a.

The semiconductor film 103 a and the charge accumulating layer 105 areformed of different materials with the first insulating film 104interposed therebetween. In this case, the semiconductor film 103 a andthe charge accumulating layer 105 have different band gaps (the band gapis an energy difference between the lower end Ec of a conduction bandand the upper end Ev of a valence band), and the charge accumulatinglayer 105 has a smaller band gap than the semiconductor film 103 a. Forexample, when the semiconductor film 103 a is formed of silicon (1.12eV), the charge accumulating layer 105 can be formed of germanium (0.72eV) or silicon germanium (0.73 to 1.1 eV). In this case, the energybarrier against an electron, i.e., a first barrier Be1 and a secondbarrier Be2 have different values, satisfying Be2>Be1.

Electrons are injected in the charge accumulating layer 105 by a methodusing hot electrons or a method using F-N type tunnel current. In a caseof using hot electrons, positive voltage is applied to the conductivefilm 113 a functioning as a gate electrode. When high voltage is appliedto a drain in this state to generate hot electrons, hot electrons thatcan overcome the first barrier can be injected in the chargeaccumulating layer 105. In a case of using F-N type tunnel current, itis not necessary to give electrons the energy to overcome the firstbarrier and electrons are injected in the charge accumulating layer 105by the quantum tunnel phenomenon.

While electrons are held in the charge accumulating layer 105, thresholdvoltage of a transistor shifts to the positive side. This state can beregarded as a state in which information “0” has been written. Theinformation “0” can be detected by a sensing circuit which detects thatthe transistor is not turned on when gate voltage to turn on thetransistor is applied in a state that charges are not held in the chargeaccumulating layer 105.

The characteristic of holding electrons accumulated in the chargeaccumulating layer 105 is important. By increasing the second barrierBe2, electrons flowing to the semiconductor film 103 a by the quantumtunnel current can be decreased stochastically and moreover, electronsflowing to the conductive film 113 a through the second insulating film104 can also be decreased. That is to say, as a method for holdingelectrons accumulated in the charge accumulating layer 105 for a longperiod of time, by increasing the second barrier Be2 to exceed the firstbarrier Be1, it is possible to prevent the charges from flowing to thesemiconductor film 103 a to disappear in a state of storage holding atwhich voltage is not applied to the conductive film 113 a.

By providing the storage element with the aforementioned structure,charges can be easily injected from the semiconductor film to the chargeaccumulating layer, and moreover, charge disappearance from the chargeaccumulating layer can be prevented. That is to say, in a case ofoperating as a memory, highly-efficient writing is possible at lowvoltage, and the charge holding characteristic can be improved.

Embodiment Mode 3

Embodiment Mode 3 will explain a manufacturing method of a nonvolatilesemiconductor storage device which is different from that in the aboveembodiment mode, with reference to drawings. Specifically, a case ofusing an insulating film including dispersed particles as a chargeaccumulating layer will be explained.

First, the island-shaped semiconductor films 103 a and 103 b are formedover the substrate 101 with the insulating film 102 interposedtherebetween, and the first insulating film 104 is formed on thesurfaces of the semiconductor films 103 a and 103 b by high-densityplasma treatment (FIG. 3A). A specific formation method may be similarto the steps shown in FIGS. 1A and 1B.

Subsequently, an insulating film 106 b (charge accumulating layer 106 b)having such a property as to trap charges is formed so as to cover theinsulating film 104. The insulating film 106 b is preferably formed byusing an insulating film having defects for trapping charges in thefilm, or an insulating film including conductive particles orsemiconductor particles 106 a (hereinafter also referred to as dispersedparticles 106 a). For example, a germanium oxide (GeO_(x)) film, agermanium nitride (GeN_(x)) film, or the like can be used (FIG. 3B). Asthe charge accumulating layer 106 b including the dispersed particles106 a, for example, an insulating film including a metal element can beused; specifically, a metal oxide film, a metal nitride film, a metalfilm including oxygen and nitrogen, or the like can be used. As thedispersed particles 106 a, particles of germanium (Ge), asilicon-germanium alloy, or the like can be included.

For example, as the charge accumulating layer 106 b, an insulating filmincluding germanium can be formed with a thickness of 1 to 20 nm,preferably 5 to 10 nm, in an atmosphere including a germanium element(for example, GeH₄) by a plasma CVD method. As the insulating filmincluding germanium, a germanium oxide (GeO_(x)) film, a germaniumnitride (GeN_(x)) film, or the like can be formed in an atmosphereincluding GeH₄ and oxygen and/or nitrogen by a plasma CVD method.

When the semiconductor film is formed of a material containing Si as itsmain component and the charge accumulating layer is formed by aninsulating film which includes germanium (for example, GeN_(x)) andwhich has defects for trapping charges in the film, or an insulatingfilm including germanium particles, over the semiconductor film with theinsulating film functioning as a tunnel oxide film interposedtherebetween, carriers injected from the semiconductor film through theinsulating film are held by being trapped in the defects or thegermanium particles in the charge accumulating layer.

After that, by the steps shown in FIGS. 1D to 2E as aforementioned, anonvolatile semiconductor storage device having a storage element can bemanufactured (FIG. 3C).

As shown in this embodiment mode, when the charge accumulating layer isformed by using the insulating film having defects for trapping chargesin the film or the insulating film including dispersed particles, evenin a case where the insulating film functioning as a tunnel oxide filmhas a defect, it is possible to prevent all the charges accumulated inthe charge accumulating layer from flowing out from the defect of theinsulating film to the semiconductor film. The charge accumulating layerformed by a germanium oxide film or a germanium nitride film includingdispersed particles has its energy band formed by the dispersedparticles as shown in FIGS. 15A and 15B, thereby obtaining a similaroperation effect. Thus, by using the structure shown in this embodimentmode, a storage element with high reliability in which data can beeasily written and accumulated charges do not easily disappear can beobtained.

Embodiment Mode 4

Embodiment Mode 4 will explain a manufacturing method of a nonvolatilesemiconductor storage device, which is different from that in the aboveembodiment mode, with reference to drawings.

First, the island-shaped semiconductor films 103 a and 103 b are formedover the substrate 101 with the insulating film 102 interposedtherebetween. Then, the insulating film 104, the charge accumulatinglayer 106 b, and the insulating film 107 are formed so as to cover theisland-shaped semiconductor films 103 a and 103 b (FIG. 4A). Themanufacturing method can be similar to that shown in FIGS. 1A to 1D.Although the charge accumulating layer shown in Embodiment Mode 2 isused as the charge accumulating layer in this embodiment mode, thecharge accumulating layer 105 shown in Embodiment Mode 1 may be used.

Next, the resist 108 is selectively formed so as to cover at least apart of an element included in a memory portion. Then, the insulatingfilm 104, the charge accumulating layer 105, and the insulating film 107which are formed over the element included in the memory portion andwhich are not covered with the resist 108, and those formed over anelement included in a logic portion are selectively removed (FIG. 4B).Here, after selectively forming the resist 108 so as to cover at least apart of the insulating film 107 formed over the semiconductor film 103a, the insulating film 104, the charge accumulating layer 105, and theinsulating film 107 which are formed over the semiconductor film 103 aand which are not covered with the resist 108, and those formed over thesemiconductor film 103 b are selectively removed, thereby partiallyexposing a surface of a part of the semiconductor film 103 a and asurface of the semiconductor film 103 b.

Subsequently, oxidation treatment, nitridation treatment, oroxynitridation treatment is performed by high-density plasma treatment(FIG. 4C). As a result, the insulating film 110 is formed on the surfaceof the insulating film 107 and the insulating film 109 is formed on theexposed surfaces of the semiconductor films 103 a and 103 b. Here, theinsulating film 110 having a film including oxygen and nitrogen (here, asilicon nitride oxide film or a silicon oxynitride film) is formed onthe surface of the insulating film 107 by performing high-density plasmatreatment under an oxygen atmosphere on the insulating film 107 formedby a silicon nitride film or a silicon nitride oxide film. At the sametime, the insulating film 109 having a silicon oxide film is formed onthe surface of the semiconductor film 103 b. It is to be noted that thehigh-density plasma treatment can be performed by the condition and themethod shown in FIG. 1B.

Subsequently, a conductive film is formed over the semiconductor films103 a and 103 b (FIG. 4D). Here, an example is shown in which a stack ofthe conductive film 111 a and the conductive film 111 b is formed as theconductive film. The conductive film may have a single-layer structureor a stacked-layer structure including three or more layers.

Each of the conductive films 111 a and 111 b can be formed of an elementselected from tantalum (Ta), tungsten (W), titanium (Ti), molybdenum(Mo), aluminum (Al), copper (Cu), chromium (Cr), niobium (Nb), and thelike or an alloy or compound material including any of these elements asits main component. Moreover, a semiconductor material typified bypolycrystalline silicon doped with an impurity element such asphosphorus can be used. Here, the conductive film 111 a is formed oftantalum nitride and the conductive film 111 b is formed of tungstenover the conductive film 111 a. In addition, the conductive film 111 acan be formed of tungsten nitride, molybdenum nitride, or titaniumnitride, and the conductive film 111 b can be formed of tantalum,molybdenum, titanium, or the like. The conductive films 111 a and 111 bcan be formed by combining these materials freely.

Next, the resist 112 is selectively formed over the conductive film 111b formed over the semiconductor films 103 a and 103 b. Then, theinsulating film 104, the charge accumulating layer 105, the insulatingfilm 107, the insulating film 110, and the conductive films 111 a and111 b which are provided over the semiconductor film 103 a, and theinsulating film 109 and the conductive films 111 a and 111 b which areprovided over the semiconductor film 103 b are selectively removed byusing the resist 112 as a mask (FIG. 5A).

In this embodiment mode, the resist 112 provided over the semiconductorfilm 103 a is formed so that the width of the resist 112 isapproximately equal to or smaller than the width of the stacked-layerstructure of the insulating film 104, the charge accumulating layer 105,the insulating film 107, and the insulating film 110 which are formedunder the conductive films 111 a and 111 b. As a result, the width ofthe obtained conductive film 113 a is approximately equal to or smallerthan the width of the stacked-layer structure of the insulating film104, the charge accumulating layer 105, the insulating film 107, and theinsulating film 110 which are formed under the conductive films 111 aand 111 b.

Next, an impurity element is introduced in the semiconductor film 103 aand the semiconductor film 103 b; thus, the impurity regions 114 a whichcan function as source or drain regions are formed in the semiconductorfilm 103 a and the semiconductor film 103 b and the channel formationregions 114 b are each formed between the impurity regions 114 a thatare provided apart from each other (FIG. 5B). The impurity regions 114 aand the channel formation regions 114 b can be formed in thesemiconductor film 103 b in a self-aligning manner by using theconductive film 113 b functioning as a gate electrode as a mask when theimpurity element is introduced in the semiconductor film 103 b.

Next, an insulating film is formed over the semiconductor films 103 aand 103 b and the conductive films 113 a and 113 b (FIG. 5C). Here, anexample is shown in which the insulating film is formed by stacking theinsulating film 115 a and the insulating film 115 b. Alternatively, theinsulating film may have a single-layer structure or a stacked-layerstructure including three or more layers. After that, contact holes areselectively formed in the insulating films 115 a and 115 b to expose thesemiconductor films 103 a and 103 b, and then the conductive film 116 isselectively formed so as to fill the contact holes. The conductive film116 is electrically connected to the impurity regions 114 a of thesemiconductor films 103 a and 103 b.

When the width of the conductive film 113 a formed over thesemiconductor film 103 a is smaller than the width of the stacked-layerstructure of the insulating film 104, the charge accumulating layer 105,the insulating film 107, and the insulating film 110, low-concentrationimpurity regions 117 in each of which an impurity element is introducedat lower concentration than in the impurity regions 114 a can be formedin the semiconductor film 103 a by controlling the condition forintroducing the impurity element in the semiconductor films 103 a and103 b in FIG. 5B (FIG. 6A). The low-concentration impurity region isformed in a part of the semiconductor film 103 a that is under theinsulating film 104 and is also under a region where the conductive film113 a does not overlap with the insulating film 104, the chargeaccumulating layer 105, the insulating film 107, and the insulating film110 (a region where the channel formation region 114 b does not overlapwith the conductive film 113 a).

After that, the insulating films 115 a and 115 b and the conductive film116 are formed similarly to FIG. 5C, thereby obtaining a nonvolatilesemiconductor storage device having a storage element (FIG. 6B).

This embodiment mode can be freely combined with any of the aboveembodiment modes.

Embodiment Mode 5

With reference to drawings, Embodiment Mode 5 will explain amanufacturing method of a semiconductor device, in which formation of aninsulating film, a conductive film, or a semiconductor film and plasmatreatment are performed continuously in a manufacturing process of anonvolatile semiconductor storage device.

When formation of an insulating film, a conductive film, or asemiconductor film and plasma treatment are performed continuously, anapparatus equipped with a plurality of chambers can be used. An exampleof the apparatus equipped with a plurality of chambers is shown in FIG.7A. It is to be noted that FIG. 7A is a top view of a structure exampleof the apparatus shown in this embodiment mode (continuousfilm-formation system).

The apparatus shown in FIG. 7A includes a first chamber 311, a secondchamber 312, a third chamber 313, a fourth chamber 314, load lockchambers 310 and 315, and a common chamber 320. Each of these chambershas airtightness and is provided with a vacuum evacuation pump and aninert gas introduction system.

The load lock chambers 310 and 315 are chambers for carrying a sample(substrate to be processed) in the system. The first to fourth chambersare chambers in which formation of a conductive film, an insulatingfilm, or a semiconductor film over the substrate 101, etching, plasmatreatment, and the like are performed. The common chamber 320 isprovided in common with the load lock chambers 310 and 315 and the firstto fourth chambers. Gate valves 322 to 327 are provided between thecommon chamber 320 and the load lock chambers 310 and 315 and betweenthe common chamber 320 and the first to fourth chambers 311 to 314. Thecommon chamber 320 is provided with a robot arm 321 by which thesubstrate 101 is delivered to each chamber.

As a specific example, described below is a case where a semiconductorfilm formed over the substrate 101 is oxidized by plasma treatment inthe first chamber 311 and nitrided by plasma treatment in the secondchamber 312, a charge accumulating layer is formed in the third chamber313, and an insulating film is formed in the fourth chamber 314.

First, a cassette 328 housing a plurality of substrates 101 is carriedin the load lock chamber 310. After the cassette 328 is carried therein,a door of the load lock chamber 310 is closed. In this state, the gatevalve 322 is opened to take out one substrate to be processed from thecassette 328, and then the substrate is disposed in the common chamber320 by the robot arm 321. Alignment of the substrate 101 is performed inthe common chamber 320 at this time.

Next, the gate valve 322 is closed and the gate valve 324 is then openedto transfer to the first chamber 311, the substrate 101 where theisland-shaped semiconductor film is formed. In the first chamber 311,first high-density plasma treatment is performed. Here, the firsthigh-density plasma treatment is performed under an oxygen atmosphere inthe first chamber 311 to form an oxide film on a surface of thesemiconductor film. The first high-density plasma treatment may beperformed under the condition shown in Embodiment Mode 1.

Next, the substrate 101 is taken out to the common chamber 320 by therobot arm 321, and transferred to the second chamber 312. In the secondchamber 312, second high-density plasma treatment is performed. Here,the second high-density plasma treatment is performed under a nitrogenatmosphere to nitride the oxide film formed on the surface of thesemiconductor film.

Subsequently, the substrate 101 is taken out to the common chamber 320by the robot arm 321 and transferred to the third chamber 313. In thethird chamber 313, the charge accumulating layer is formed by a plasmaCVD method. The charge accumulating layer may be formed of the materialshown in Embodiment Mode 1 or 2. Here, a film including germanium isformed by a plasma CVD method. Although the example of using a plasmaCVD method is shown here, a sputtering method using a target may also beemployed.

Next, the substrate 101 is taken out to the common chamber 320 by therobot arm 321 and transferred to the fourth chamber 314. In the fourthchamber 314, an insulating film is formed by a plasma CVD method. Forexample, an insulating film including nitrogen is formed by a plasma CVDmethod.

Then, the substrate 101 is transferred to the load lock chamber 315 bythe robot arm 321 and housed in a cassette 329.

It is to be noted that FIG. 7A shows just one example, and the number ofchambers can be increased further. Although FIG. 7A shows the example ofusing single-type chambers as the first to fourth chambers 311 to 314,batch-type chambers may be used to process plural substrates at onetime.

By using the apparatus shown in this embodiment mode in this manner, theformation of a conductive film, an insulating film, or a semiconductorfilm and the high-density plasma treatment can be performed continuouslywithout exposure to the air. This can achieve prevention of impuritymixture and improvement of production efficiency.

Next, in the present invention, an example of an apparatus in the caseof performing high-density plasma treatment is explained with referenceto FIG. 7B.

The apparatus shown in FIG. 7B includes a support 351 for having anobject 331 to be processed disposed thereon, on which high-densityplasma treatment is to be performed; a gas supplying portion 352 forintroducing gas; an evacuation port 353; an antenna 354; a dielectricplate 355; and a high-frequency supplying portion 356 which supplieshigh frequency for high-density plasma generation. Moreover, thetemperature of the object 331 to be processed can be controlled when thesupport 351 is provided with a temperature controlling portion 357. Anexample of the high-density plasma treatment is hereinafter explained.Any object on which plasma treatment is performed in the aboveembodiment mode can be used as the object to be processed.

First, the processing chamber is made vacuum and a gas including oxygenor nitrogen is introduced from the gas supplying portion 352. Forexample, as the gas including oxygen, a mixed gas of oxygen (O₂) and anoble gas or a mixed gas of oxygen, hydrogen, and a noble gas can beintroduced. As the gas including nitrogen, a mixed gas of nitrogen and anoble gas or a mixed gas of NH₃ and a noble gas can be introduced. Next,the object 331 to be processed is disposed on the support 351 having thetemperature controlling portion 357 and the object 331 to be processedis heated at temperatures ranging from 100° C. to 550° C. It is to benoted that the distance between the object 331 to be processed and thedielectric plate 355 ranges from 20 to 80 mm (preferably 20 to 60 mm).

Next, a microwave is supplied from the high-frequency supplying portion356 to the antenna 354. Here, a microwave with a frequency of 2.45 GHzis supplied. Then, the microwave is introduced in the processing chamberfrom the antenna 354 through the dielectric plate 355; thus,high-density plasma 358 activated by plasma excitation is generated. Forexample, when plasma treatment is performed in an atmosphere includingan NH₃ gas and an Ar gas, high-density excited plasma in which the NH₃gas and the Ar gas are mixed is generated by the microwave. In thehigh-density excited plasma in which the NH₃ gas and the Ar gas aremixed, the introduced microwave makes the Ar gas excited to generateradicals (Ar.), and when the Ar radicals and NH₃ molecules collide witheach other, radicals (NH.) are generated. This NH. and the object 331 tobe processed react with each other, thereby nitriding the object 331 tobe processed. After that, the NH₃ gas and the Ar gas are exhausted tothe outside of the processing chamber from the evacuation port 353.

By performing the plasma treatment using the apparatus shown in FIG. 7Bin this manner, the object to be processed with little plasma damage canbe formed because the electron temperature is low (1.5 eV or less) andthe electron density is high (1×10¹¹ cm⁻³ or more).

It is to be noted that this embodiment mode can be freely combined withany of the above embodiment modes.

Embodiment Mode 6

Embodiment Mode 6 will explain a manufacturing method of a nonvolatilesemiconductor storage device, which is different from that in the aboveembodiment mode, with reference to drawings. Specifically, descriptionis made of a case in which gate insulating films of plural transistorsprovided in a logic portion have different thickness in a semiconductordevice having a memory portion and the logic portion.

When plural functional circuits are provided by using plural thin filmtransistors in the logic portion, it may be preferable to form gateinsulating films of the thin film transistors provided in the respectivefunctional circuits with different thickness because each circuitdemands a different characteristic. For example, in order to reducedrive voltage and variation in threshold voltage, the thin filmtransistor preferably has a thin gate insulating film. Meanwhile, inorder to increase the drive voltage and voltage withstanding property ofthe gate insulating film, the thin film transistor preferably has athick gate insulating film. For example, a thin insulating film formedby the high-density plasma treatment shown in the above embodiment modeis applied to a circuit of which drive voltage and variation inthreshold voltage are demanded to be low. On the contrary, a thickinsulating film is applied to a circuit of which drive voltage andvoltage withstanding property of the gate insulating film are demandedto be high. Description is hereinafter made with reference to drawings.

First, the island-shaped semiconductor film 103 a, the island-shapedsemiconductor film 103 b, and an island-shaped semiconductor film 103 care formed over the substrate 101 with the insulating film 102interposed therebetween (FIG. 9A). Here, the semiconductor film 103 a isincluded in an element of the memory portion while the semiconductorfilm 103 b and the semiconductor film 103 c are included in elements ofthe logic portion.

Each of the semiconductor films 103 a and 103 b is preferably formed byusing a crystalline semiconductor film. The crystalline semiconductorfilm includes one obtained by crystallizing an amorphous semiconductorfilm formed over the insulating film 102 through thermal treatment orlaser irradiation, one obtained by making a crystalline semiconductorfilm formed over the insulating film 102 into amorphous andrecrystallizing it, and so on.

When the crystallization or the recrystallization is conducted by laserirradiation, an LD-pumped continuous wave (CW) laser (YVO₄, secondharmonic (wavelength: 532 nm)) can be used as a laser light source. Thewavelength is not necessarily limited to the second harmonic; however,the second harmonic is superior to other higher harmonics in point ofenergy efficiency. When a semiconductor film is irradiated with CW laserlight, the semiconductor film continuously receives energy; therefore,once the semiconductor film is melted, the melted state can continue.Moreover, it is possible to move a solid-liquid interface of thesemiconductor film by scanning CW laser light and to form a crystalgrain which is long in one direction along this moving direction. Asolid-state laser is used because its output is so stable that a stableprocess can be expected as compared with a gas laser or the like. Notonly a CW laser but also a pulsed laser with a repetition rate of 10 MHzor more can be used. In a case of using a pulsed laser with highrepetition rate, when the pulse interval is shorter than the periodafter the semiconductor film is melted and before the meltedsemiconductor film is solidified, the semiconductor film can normallymaintain a melting state. Then, by moving the solid-liquid interface,the semiconductor film including a crystal grain which is long in onedirection can be formed. Another CW laser or pulsed laser with arepetition rate of 10 MHz or more can also be used. For example, as thegas laser, an Ar laser, a Kr laser, a CO₂ laser, or the like is given.As the solid-state laser, a YAG laser, a YLF laser, a YAlO₃ laser, aGdVO₄ laser, a KGW laser, a KYW laser, an alexandrite laser, aTi:sapphire laser, a Y₂O₃ laser, a YVO₄ laser, or the like is given.Moreover, a ceramic laser such as a YAG laser, a Y₂O₃ laser, a GdVO₄laser, or a YVO₄ laser is given. As a metal vapor laser, ahelium-cadmium laser or the like is given. Moreover, oscillation oflaser light with TEM₀₀ (single transverse mode) in a laser oscillator ispreferable because the energy homogeneity of a linear beam spot on anirradiation surface can be raised. In addition, a pulsed excimer lasermay be used.

Subsequently, the insulating film 104, the charge accumulating layer105, and the insulating film 107 are formed over the semiconductor films103 a to 103 c (FIG. 9B).

The insulating film 104 is formed with a thickness of 1 to 10 nm,preferably 5 to 10 nm, by performing oxidation treatment or nitridationtreatment on the semiconductor films 103 a to 103 c by high-densityplasma treatment. Here, a silicon oxide film is formed on surfaces ofthe semiconductor films 103 a to 103 c by performing oxidation treatmentby high-density plasma treatment using a material containing Si as itsmain component for the semiconductor films 103 a to 103 c, and thennitridation treatment is performed by high-density plasma treatment toform a film including oxygen and nitrogen on a surface of the siliconoxide film.

The charge accumulating layer 105 is provided over the insulating film104. The charge accumulating layer 105 is preferably formed of amaterial with a smaller energy gap (band gap) than the material used forthe semiconductor films 103 a and 103 b. Here, the charge accumulatinglayer 105 is formed by a film containing germanium as its main componentwith a thickness of 1 to 20 nm, preferably 5 to 10 nm, in an atmosphereincluding GeH₄ by a plasma CVD method. The charge accumulating layershown in Embodiment Mode 3 may be used as the charge accumulating layer105.

When each of the semiconductor films 103 a to 103 c is formed of thematerial containing Si as its main component and the film includinggermanium with a smaller energy gap than Si is provided as the chargeaccumulating layer 105 over the semiconductor films 103 a to 103 c withthe insulating film 104 functioning as a tunnel oxide film interposedtherebetween, a second barrier formed by the insulating film 104 againsta charge of the charge accumulating layer 105 gets higher in energy thana first barrier formed by the insulating film 104 against a charge ofthe semiconductor film 103 a. As a result, charges can be easilyinjected from the semiconductor film 103 a to the charge accumulatinglayer 105 and charge disappearance from the charge accumulating layer105 can be prevented. That is to say, in a case of operating as amemory, highly-efficient writing is possible at low voltage andmoreover, the charge holding characteristic can be improved.

The insulating film 107 is formed over the charge accumulating layer 105by using a silicon oxynitride film, a silicon nitride film, a siliconnitride oxide film, or the like. Here, the insulating film 107 is formedby using a silicon nitride film or a silicon nitride oxide film with athickness of 1 to 20 nm, preferably 5 to 10 nm, by a plasma CVD method.Alternatively, the charge accumulating layer 105 may be subjected tohigh-density plasma treatment under a nitrogen atmosphere to performnitridation treatment so that a nitride film (for example, GeN_(x) in acase of using a film containing germanium as its main component as thecharge accumulating layer 105) is formed on a surface of the chargeaccumulating layer 105. In the latter case, the nitride film obtained bythe nitridation treatment may be used as the insulating film 107 or theaforementioned insulating film may be separately formed as theinsulating film 107 over the nitride film obtained by the nitridationtreatment. In addition, the insulating film 107 may be formed ofaluminum oxide (AlO_(x)), hafnium oxide (HfO_(x)), or tantalum oxide(TaO_(x)).

Next, after selectively forming the resist 108 so as to cover theelement included in the memory portion, the insulating film 104, thecharge accumulating layer 105, and the insulating film 107, which areformed over the element included in the logic portion, are selectivelyremoved (FIG. 9C). Here, after selectively forming the resist 108 so asto cover the insulating film 107 formed over the semiconductor film 103a, the insulating film 104, the charge accumulating layer 105, and theinsulating film 107, which are formed over the semiconductor films 103 band 103 c, are selectively removed, thereby exposing the semiconductorfilms 103 b and 103 c.

Next, oxidation treatment, nitridation treatment, or oxynitridationtreatment is performed by high-density plasma treatment (FIG. 10A). As aresult, the insulating film 110 is formed on a surface of the insulatingfilm 107 formed over the semiconductor film 103 a, and the insulatingfilm 109 is formed on surfaces of the semiconductor films 103 b and 103c. Here, the insulating film 110 having a film including oxygen andnitrogen (here, a silicon nitride oxide film or a silicon oxynitridefilm) is formed on the surface of the insulating film 107 by performinghigh-density plasma treatment under an oxygen atmosphere on theinsulating film 107 which is formed by a silicon nitride film or asilicon nitride oxide film. At the same time, the insulating film 109having a silicon oxide film is formed on the surface of thesemiconductor film 103 b.

Subsequently, a conductive film is formed over the semiconductor films103 a to 103 c. Then, the resist 112 is selectively formed over theconductive film positioned over the semiconductor films 103 a and 103 b.By selectively etching the conductive film, the conductive films 113 aand 113 b are formed over the semiconductor films 103 a and 103 b, andthe conductive film formed over the semiconductor film 103 c is removed(FIG. 10B). The conductive films 113 a and 113 b can be formed of thematerial used for the conductive films 111 a and 111 b shown in theabove embodiment mode.

Next, an insulating film 121 is formed so as to cover the exposedsurfaces of the semiconductor films 103 a to 103 c and the conductivefilms 113 a and 113 b, and then a conductive film 122 is formed over theinsulating film 121 (FIG. 10C). The insulating film 121 functions as agate insulating film of a thin film transistor including thesemiconductor film 103 c.

Next, a resist 123 is selectively formed over the conductive film 122formed over the semiconductor film 103 c. Then, the conductive film 122and the insulating film 121 are selectively removed by using the resist123 as a mask (FIG. 11A).

Next, an impurity element is introduced in the semiconductor films 103 ato 103 c; thus, the impurity regions 114 a which can function as sourceor drain regions are formed in the semiconductor films 103 a to 103 cand the channel formation regions 114 b are each formed between theimpurity regions 114 a that are provided apart from each other (FIG.11B). The impurity regions 114 a and the channel formation regions 114 bcan be formed in a self-aligning manner by using as a mask theconductive films 113 a, 113 b, and 124 functioning as gate electrodeswhen the impurity element is introduced in the semiconductor films 103 ato 103 c.

Subsequently, an insulating film is formed over the conductive films 113a, 113 b, and 124 and the exposed semiconductor films 103 a to 103 c(FIG. 11C). Here, an example of a stack of the insulating film 115 a andthe insulating film 115 b is shown as the insulating film. Theinsulating film may have a single-layer structure or a stacked-layerstructure including three or more layers. After that, contact holes areselectively formed in the insulating films 115 a and 115 b to expose thesemiconductor films 103 a to 103 c, and then the conductive film 116 isselectively formed so as to fill the contact holes. The conductive film116 is electrically connected to the impurity regions 114 a of thesemiconductor films 103 a to 103 c.

This embodiment mode can be freely combined with any of the aboveembodiment modes.

Embodiment Mode 7

Embodiment Mode 7 will describe an application example of asemiconductor device which is provided with the nonvolatilesemiconductor storage device shown in the above embodiment mode and inwhich data can be inputted/outputted without contact, with reference todrawings. The semiconductor device in which data can beinputted/outputted without contact is also referred to as an RFID tag,an ID tag, an IC tag, an IC chip, an RF tag, a wireless tag, anelectronic tag, or a wireless chip depending on the usage.

First, an example of a top-surface structure of a semiconductor deviceshown in this embodiment mode is explained with reference to FIG. 12A. Asemiconductor device 80 shown in FIG. 12A includes a thin filmintegrated circuit 131 provided with a plurality of elements included ina memory portion and a logic portion, and a conductive film 132functioning as an antenna. The conductive film 132 functioning as anantenna is electrically connected to the thin film integrated circuit131. Although this embodiment mode shows an example in which theconductive film 132 functioning as an antenna is provided in a coil-likeshape and an electromagnetic induction method or an electromagneticcoupling method is applied, the semiconductor device of the presentinvention is not limited to this, and a microwave method can also beapplied. In a case of a microwave method, the shape of the conductivefilm 132 functioning as an antenna may be appropriately determineddepending on the wavelength of an electromagnetic wave to be used.

FIG. 12B is a schematic view of a cross section of FIG. 12A. Theconductive film 132 functioning as an antenna may be provided over theelements included in the memory portion and the logic portion; forexample, the conductive film 132 functioning as an antenna can beprovided over the insulating film 115 b with the insulating film 133interposed therebetween in the structure shown in the above embodimentmode.

Next, an operation of the semiconductor device shown in this embodimentmode is explained.

The semiconductor device 80 has a function of exchanging data withoutcontact, and includes a high-frequency circuit 81, a power sourcecircuit 82, a reset circuit 83, a clock generating circuit 84, a datademodulating circuit 85, a data modulating circuit 86, a controllingcircuit 87 for controlling another circuit, a storage circuit 88, and anantenna 89 (FIG. 13A). The high-frequency circuit 81 receives a signalfrom the antenna 89 and outputs a signal, which is received from thedata modulating circuit 86, from the antenna 89. The power sourcecircuit 82 generates a power source potential from a received signal.The reset circuit 83 generates a reset signal. The clock generatingcircuit 84 generates various clock signals based on a received signalinputted from the antenna 89. The data demodulating circuit 85demodulates a received signal and outputs the demodulated signal to thecontrolling circuit 87. The data modulating circuit 86 modulates asignal received from the controlling circuit 87. As the controllingcircuit 87, for example, a code extracting circuit 91, a code judgingcircuit 92, a CRC judging circuit 93, and an output unit circuit 94 areprovided. It is to be noted that the code extracting circuit 91 extractseach of plural codes included in an instruction sent to the controllingcircuit 87. The code judging circuit 92 judges the content of theinstruction by comparing the extracted code with a code corresponding toa reference. The CRC judging circuit 93 detects whether or not there isa transmission error or the like based on the judged code.

Subsequently, an example of an operation of the aforementionedsemiconductor device is explained. First, a wireless signal is receivedby the antenna 89 and then sent to the power source circuit 82 throughthe high-frequency circuit 81, thereby generating a high power sourcepotential (hereinafter referred to as VDD). The VDD is supplied to eachcircuit in the semiconductor device 80. A signal sent to the datademodulating circuit 85 through the high-frequency circuit 81 isdemodulated (hereinafter this signal is called a demodulated signal).Moreover, signals passed through the reset circuit 83 and the clockgenerating circuit 84 via the high-frequency circuit 81, and thedemodulated signal are sent to the controlling circuit 87. The signalssent to the controlling circuit 87 are analyzed by the code extractingcircuit 91, the code judging circuit 92, the CRC judging circuit 93, andthe like. Then, based on the analyzed signals, the information of thesemiconductor device stored in the storage circuit 88 is outputted. Theoutputted information of the semiconductor device is encoded through theoutput unit circuit 94. Further, the encoded information of thesemiconductor device 80 passes through the data modulating circuit 86and then is sent by the antenna 89 as a wireless signal. It is to benoted that a low power source potential (hereinafter called VSS) iscommon in the plural circuits included in the semiconductor device 80and VSS can be GND.

In this manner, when a signal is sent from a reader/writer to thesemiconductor device 80 and the signal sent from the semiconductordevice 80 is received by the reader/writer, the data in thesemiconductor device can be read.

Moreover, in the semiconductor device 80, power source voltage may besupplied to each circuit by electromagnetic waves without mounting apower source (battery), or a power source (battery) may be mounted sothat power supply voltage is supplied to each circuit by bothelectromagnetic waves and the power source (battery).

Next, an example of usage of a semiconductor device in which data can beinputted/outputted without contact is explained. A side surface of amobile terminal including a display portion 3210 is provided with areader/writer 3200. A side surface of a product 3220 is provided with asemiconductor device 3230 (FIG. 13B). When the reader/writer 3200 isheld over the semiconductor device 3230 included in the product 3220,the display portion 3210 displays information on the product, such as amaterial, a production area, an inspection result for each productionstep, history of circulation process, and description of the product. Inaddition, when a product 3260 is transferred by a conveyer belt, theproduct 3260 can be inspected by using a semiconductor device 3250provided to the product 3260 and a reader/writer 3240 (FIG. 13C). Inthis manner, by using the semiconductor device in the system,information can be obtained easily and higher performance and highervalue addition are achieved.

In addition to the above, the semiconductor device provided with thenonvolatile semiconductor storage device of the present invention can beapplied in a wide range. The semiconductor device can be applied to anyproduct in which the information such as history of an object can beclarified without contact effectively for production, management, and soon. For example, the semiconductor device of the present invention canbe provided and used for bills, coins, securities, certificates, bearerbonds, containers for wrapping, books, storage media, personalbelongings, vehicles, groceries, garments, health products, dailycommodities, medicines, electronic appliances, and the like. Examples ofthese are explained with reference to FIGS. 14A to 14H.

The bills and coins are money that circulates in the market, and includeone that can be used in the same way as money in a specific area (suchas cash voucher), a commemorative coin, and the like. The securitiesindicate a check, certificate, a promissory note, and the like (see FIG.14A). The certificates indicate a driver's license, a resident's card,and the like (see FIG. 14B). The bearer bonds indicate a stamp, a ricecoupon, various gift coupons, and the like (see FIG. 14C). Thecontainers for wrapping indicate a wrapper for a packaged lunch and thelike, a plastic bottle, and the like (see FIG. 14D). The books indicatea paperback book, a hardback book, and the like (see FIG. 14E). Thestorage media indicate DVD software, a video tape, and the like (seeFIG. 14F). The vehicles indicate a wheeled vehicle such as a bicycle, aship, and the like (see FIG. 14G). The personal belongings indicate abag, glasses, and the like (see FIG. 14H). The groceries indicate foods,beverages, and the like. The garments indicate clothes, shoes, and thelike. The health products indicate a medical apparatus, a healthappliance, and the like. The daily commodities indicate furniture, alighting apparatus, and the like. The medicines indicate a drug, anagricultural chemical, and the like. The electronic appliances indicatea liquid crystal display device, an EL display device, a televisiondevice (television receiver or thin television receiver), a cellularphone, and the like.

By providing the semiconductor device 80 for bills, coins, securities,certificates, bearer bonds, and the like, falsification thereof can beprevented. In addition, by providing the semiconductor device 80 tocontainers for wrapping, books, storage media, personal belongings,groceries, daily commodities, electronic appliances, and the like,efficiency of an inspection system, a system of a rental store, and thelike can be improved. By providing the semiconductor device 80 forvehicles, health products, medicines, and the like, falsification andtheft thereof can be prevented, and accidental ingestion of a drug canbe prevented in the case of the medicines. The semiconductor device 80can be provided by being attached to a surface of an article or beingimplanted in an article. For example, the semiconductor device can beimplanted in paper in the case of a book, and can be implanted in anorganic resin in the case of a package formed of the organic resin.

By providing the semiconductor devices to containers for wrapping,books, storage media, personal belongings, groceries, clothes, dailycommodities, electronic appliances, and the like, an inspection systemand a system of a rental store, and the like can be made efficient. Byproviding the semiconductor devices to vehicles, falsification and theftthereof can be prevented. By implanting the semiconductor devices increatures such as animals, identification of the individual creature canbe easily carried out. For example, by implanting the semiconductordevice equipped with a sensor in a creature such as livestock, it ispossible to easily know not only a year of birth, sex, kind and the likebut also a health condition such as current temperature.

As thus described, the semiconductor device of the present invention canbe applied in quite a wide range, and can be applied to electronicappliances of every field. This embodiment mode can be freely combinedwith any of the above embodiment modes.

This application is based on Japanese Patent Application serial no.2006-034543 filed in Japan Patent Office on Feb. 10, 2006, the entirecontents of which are hereby incorporated by reference.

1. A nonvolatile semiconductor storage device comprising: a substratehaving an insulating surface; a storage element included in a memoryportion comprising: a first semiconductor film over the substrate,having a pair of first impurity regions formed apart from each other anda first channel formation region provided between the pair of firstimpurity regions; a first insulating film provided over the firstchannel formation region; a charge accumulating layer provided over thefirst insulating film; a second insulating film provided over the chargeaccumulating layer; and a first gate electrode layer provided over thesecond insulating film; an element included in a logic portioncomprising: a second semiconductor film over the substrate, having apair of second impurity regions formed apart from each other and asecond channel formation region provided between the pair of secondimpurity regions; a third insulating film provided over the secondchannel forming region; and a second gate electrode layer provided overthe third insulating film, wherein a first energy barrier is formed bythe first insulating film against a charge of the first semiconductorfilm, wherein a second energy barrier is formed by the first insulatingfilm against a charge of the charge accumulating layer, wherein thesecond energy barrier is higher than the first energy barrier, whereinthe first insulating film and the third insulating film are differentmaterial, and wherein the first gate electrode layer and the second gateelectrode layer are the same material.
 2. The nonvolatile semiconductorstorage device according to claim 1, wherein the charge accumulatinglayer comprises germanium as a main component.
 3. The nonvolatilesemiconductor storage device according to claim 1, wherein the firstgate electrode layer and the second gate electrode layer are conductivefilms each including a nitrogen atom.
 4. A nonvolatile semiconductorstorage device comprising: a substrate having an insulating surface; astorage element included in a memory portion comprising: a firstsemiconductor film over the substrate, having a pair of first impurityregions formed apart from each other and a first channel formationregion provided between the pair of first impurity regions; a firstinsulating film provided over the first channel formation region; acharge accumulating layer provided over the first insulating film; asecond insulating film provided over the charge accumulating layer; anda first gate electrode layer provided over the second insulating film;an element included in a logic portion comprising: a secondsemiconductor film over the substrate, having a pair of second impurityregions formed apart from each other and a second channel formationregion provided between the pair of second impurity regions; a thirdinsulating film provided over the second channel forming region; and asecond gate electrode layer provided over the third insulating film,wherein the charge accumulating layer comprises a material with asmaller energy gap than the first semiconductor film, wherein the firstinsulating film and the third insulating film are different material,and wherein the first pate electrode layer and the second gate electrodelayer are the same material.
 5. The nonvolatile semiconductor storagedevice according to claim 4, wherein the charge accumulating layercomprises germanium as a main component.
 6. The nonvolatilesemiconductor storage device according to claim 4, wherein the firstgate electrode layer and the second gate electrode layer are conductivefilms each including a nitrogen atom.
 7. A nonvolatile semiconductorstorage device comprising: a substrate having an insulating surface; astorage element included in a memory portion comprising: a firstsemiconductor film formed over the substrate, having a pair of impurityregions formed apart from each other and a channel formation regionprovided between the pair of impurity regions; a first insulating filmprovided over the channel formation region; a charge accumulating layercomprises germanium, provided over the first insulating film; a secondinsulating film provided over the charge accumulating layer; and a firstgate electrode layer provided over the second insulating film; anelement included in a logic portion comprising: a second semiconductorfilm over the substrate, having a pair of second impurity regions formedapart from each other and a second channel formation region providedbetween the pair of second impurity regions; a third insulating filmprovided over the second channel forming region; and a second gateelectrode layer provided over the third insulating film, wherein thefirst insulating film and the third insulating film are differentmaterial, and wherein the first gate electrode layer and the second gateelectrode layer are the same material.
 8. The nonvolatile semiconductorstorage device according to claim 7 wherein the first insulating filmcomprises: an oxide film; and a film including oxygen and nitrogen overthe oxide film.
 9. The nonvolatile semiconductor storage deviceaccording to claim 7 wherein the charge accumulating layer furthercomprises nitrogen.
 10. The nonvolatile semiconductor storage deviceaccording to claim 7 wherein a surface of the second insulating film isoxidized.
 11. The nonvolatile semiconductor storage device according toclaim 7 wherein the semiconductor film further has a low-concentrationimpurity region between the impurity region and the channel formationregion.